Abstract: Dynamic thermogravimetric analysis (TGA) of two kinds of cyanate/epoxy blends was performed. The effects of molar ratios of cyanate and epoxy on thermal stability were disclosed. Coats-Redfern Equation was used to compute the weight loss data and calculate the activation energies of decomposition. It is found that the cyanate-rich blends containing bisphenol A diglycidyl ether have a two step decomposition process and epoxy-rich blends have a single mechanism. The activation energy of thermal decomposition of the blends containing novolac epoxy, which is greater than that of the blends containing bisphenol A diglycidyl ether, is independent of the temperature and concentration of the epoxy, indicating much better thermal stability than that of the blends containing bisphenol A diglycidyl ether.